Iwa international Specialist Conference

17.

PROPOSED ABSTRACT

IWA International Specialist Conference

BIOSOLIDS 2003-Wastewater Sludge as a Resource

Norwegian University of Science and Technology (NTNU), 23.-25. June, 2003

Session 7: Technologies for recovery of phosphate and other specific products from sludge
Deborah Pritchard (Australia) [e-mail]

Curtin University of Technology

Northam 6401

Western Australia

Australia

The bioavailability of phosphorus in biosolids

The recycling of P from wastewater solids is of benefit given dwindling world supplies of P, and the decline of high-grade P reserves. The agricultural land application of biosolids is a beneficial option for the use of stabilised wastewater solids (biosolids). However, to be sustainable, land application rates must optimise crop production whilst being of minimal environmental risk. The approach used in this study was to consider biosolids as a source of fertiliser P. A glasshouse study and a field trial were conducted with the objective of determining the bioavailability of phosphorus (P) in soil amended with biosolids. Biosolids were compared with inorganic P fertiliser to establish relative effectiveness (RE) values. The soils used were lateritic gravelly loams and P responsive. The anaerobically digested dewatered biosolids cake used for all experiments had 86% moisture content and 2.96% total P content. There was no chemical precipitation of P during wastewater treatment.

In the glasshouse, P uptake by wheat shoots were measured at 33 days after sowing (DAS) in pots for three consecutive crops using eight rates of monocalcium phosphate (MCP) and eight rates of biosolids to 150 mg P/kg. A similar design was applied to a 0.5 ha field trial using triple superphosphate (TSP) and biosolids with rates of P to 150 kg P/ha. Phosphorus uptake was determined in wheat shoots at four growth stages over the season and grain yield measured. Bicarbonate extractable soil P (Colwell P) was related to P uptake in both studies. Chemical P fractionation was examined in the final pot trial. Residual RE was determined in year two by applying fresh rates of TSP. Basal rates of other nutrients including nitrogen (N) were applied to ensure that P was the only limiting variable. A number of other parallel studies were included to examine differences due to incorporation on P bioavailability.
The RE of biosolids was equal to that of MCP in the glasshouse pot experiment where biosolids were fully in contact with the soil. Under field conditions the RE of biosolids was approximately half that of top-dressed TSP. Compared with drilled TSP, the RE of biosolids would be expected to be between 2-4 times less. Phosphorus bioavailability is largely influenced by the extent of incorporation. Phosphorus was unavailable to plants where biosolids were surface applied and poorly available where incorporation was poor. Biosolids did not increase available soil P as quickly as inorganic P at similar rates. Studies that rely solely on soil bicarbonate extractable P may underestimate P bioavailability in biosolids amended soils. This may also include laboratory incubation studies that measure P availability over time. In addition, standard soil sieving procedures used to estimate soil available P in the <2mm fraction of lateritic soils contributed to loss of biosolids particles, which in turn underestimated bicarbonate extractable P.
This study cannot possibly address P bioavailability associated with the many different types of wastewater solids following land application to a range of soils. However, its interactive approach using both pot and field trials allows for interpretation of existing research, in particular the method of incorporation. Analysis of both soil available P and plant uptake of P in parallel highlights limitations of soil chemical tests and laboratory incubation to assess P bioavailability. Comparison with an inorganic source of P has enabled relative effectiveness values to be estimated. This can be used to determine P loading rates specific for a given soil type using existing P fertiliser data and is applicable to either P enriched or P deficient soils. The use of a P responsive soil, combined with the addition of N and basal nutrients has attempted to ensure that P is the limiting factor, a problem affecting many biosolids studies to date.
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BIOSOLIDS 2003 - Wastewater Sludge as a Resource (23. - 25. June 2002)

Recycling of phosphorus in sewage sludge

(T. Krogstad, T. Sogn & A. Sæbø)

Abstract
An ongoing project focusing on recycling of sewage sludge has as the main goal to document the phosphorus effect of selected Norwegian sludge types regarding to plant growth. Norwegian sewage sludge has a high P content due to use of precipitation chemicals which also may influence the availability of the P in soil. Substantial documentation of the fertility effect, positive and negative, is needed before the increase recommendation for agricultural use.
Considering earlier investigations in Norwegian field experiments the following hypotheses are tested:

1. 
   Sewage sludge where P is precipitated using Fe and Al chemicals has limited P fertility effect both on the short term and the long term, and may reduce the P availability in the soil.
   
2. 
   Biological sludge (compost) has a P fertility effect comparable to animal manure or other easily soluble P fertilisers.
   

For the investigations five different sewage sludge types and compost are tested in two soil types (clay and moraine). The P in the sewage sludge is precipitated using Fe and Al chemicals and one of the sludge has a finishing treatment using lime. The total contents of P, Fe and Al vary in the interval of 0.9-3%, 0.4-13% and 0.6-4.3% respectively.

The hypotheses are tested using laboratory experiments to study the effect of sewage sludge and compost on the sorption effect of P in soil, and by using pot experiments in greenhouse where grass is grown in soil with sewage sludge and compost as P sources. Two different sludge amounts are used corresponding to a normal P fertilisation using commercial fertiliser and to the maximum allowable amount of sewage sludge in a 10 year's period (20 t per ha). The P availability is tested in the soil using standard soil availability tests before and after different cuttings of the grass. The P effect of sewage sludge and compost is compared to the P effect using commercial fertilisers. The results of the chemical tests are compared to the total amount of P removed from the soil in the grass yields.

19.

"Amendment of biosolids for agricultural applications

¹José Cárdenas, ¹Mabel Vaca*, ¹Margarita Beltrán, ¹Raymundo López y ²Blanca Jiménez

1: Universidad Autónoma Metropolitana-Azcapotzalco, Av. San Pablo No. 180, Col. Reynosa-Tamaulipas, México, D. F. 02080 e:mail: [e-mail]

2: Universidad Nacional Autónoma de México, Instituto de Ingeniería, P. O. Box 70-472, Coyoacán, México, D.F. 04510

Abstract

The biosolids disposal in land application is considered a desirable option, especially in soil restauration activities, because it returns useful nutrients and organic matter to the land and enhances humidity retention of soils. However, it requires their physical and chemical characterization as well as the addition of nutrients, such as P or K, to enhance the growth of plants. In turn, the excess of nutrients could be leached and pollute superficial or underground water. In the amendment of biosolids with natural zeolite (amonnium- homoionized clinoptilolite) and phosphoric rock , aimed to be applied in dosed fertilization for agricultural activities, was studied.

Biosolids, conditioned with lime (Ca(OH)₂, pH = 12.4) were obtained from the primary treatment of a domestic wastewater treatment plant in Mexico City. The contents of heavy metals were below the limits regulated by EPA (40 CFR , part 503), for their use in agricultural activities.

Biosolids were conditioned with three different proportions of NH₄⁺ ,and K⁺ saturated clinoptilolite (Cp), and phosphate rock (PR) mixture. Leaching of NH₄⁺, P and K form the amended biosolids, was studied using a continuous flow reactor and deionized water at1.0mL/min and controls with non-conditioned biosolids and zeolite were also set. Dosed liberation of nutrients due to ionic exchange promoted by the zeolite and slow dilution of phosphoric rock were the dominant mechanisms observed. The amended biosolids release nutrients at rates up to 50% those observed at biosolids without amendment and in quantities suitable for growth of the inteded plants. The results obtained using lettuce (Lactuca. Sativa var. Intybacea Hort) showed comparable growth (expressed as dry biomasss) to that of the control planted in a soil fertilized with commercial N and P. The main conclusion is that these biosolids can be conditioned with Cp and Rf to use them as substitutes of commercial fertilizers and can contribute to the control of pollution of water sources due to the excess of nutrients released in this last practice.

20.

EVALUATION OF THE POTENTIAL FOR BIOAEROSOLS

FROM LAND APPLIED BIOSOLIDS
I.L. Pepper, J. Brooks, B. Tanner,

K.L. Josephson, and C.P. Gerba
The University of Arizona

Tucson, AZ USA
ABSTRACT
The overall objective of this report was to quantitatively and qualitatively document the potential hazards of biological aerosols derived from biosolids, and ultimately develop risk assessment models and land-management strategies for safe, effective use of biosolids. The specific objectives were: i) Quantify bacterial and viral pathogens emitted as bioaerosols from point sources of biosolids, and area (land-applied) sources of biosolids; ii) Develop risk assessment models based on a) hazard identification, b) dose response, c) exposure assessment; d) risk characterization; and iii) Evaluate bioaerosol emissions following defined management strategies: a) incorporation of biosolids via disking, b) injection of liquid sludges.
Approximately 65% of all processed sewage is ultimately land applied as biosolids in the United States. Biosolids are generally classified with increased treatment processing as “Class B” or “Class A.” Of these categories, “Class A” biosolids can be reused with few restrictions. For “Class B” biosolids, which normally contain human pathogenic microorganisms and heavy metals of variable concentrations, there are usually site restrictions placed on biosolid-amended soils, depending on the proposed future use of the site e.g., grazing or agriculture. However, clearly the potential exists for biological aerosols and odors to be emitted from biosolids that bypass site restrictions. As such, bioaerosols represent one of the few legitimate arguments that could in some circumstances limit land application of biosolids. In this work, we are evaluating the true potential for bioaerosol emissions from biosolids, as well as documenting management strategies that minimize emissions. This work is being funded through the University of Arizona, National Science Foundation, Water Quality Center. Research has consisted of laboratory studies at the University of Arizona and field studies in Southern Arizona and Southern California. In addition, aerosol samples have been collected from wastewater treatment plants to allow for the evaluation of the safety of wastewater plant operators. Bioaerosol samples have been collected via “Impingement” using SKC biosamplers. The potential biologicals monitored for included: i) viruses: enteroviruses, calciviruses, adenoviruses; ii) phage e.g., MS2, PRD1; iii) E. coli; iv) Salmonella; v) total coliforms; vi)Clostridium perfringens; vii) Aspergillus spp.; viii) Endotoxin. Air samples have been collected at discrete distances from both biosolid piles (point sources), or land applied biosolids(area

sources). Both point source and area source models are being used to assess the transport and exposure assuming different wind speeds and survival of the pathogen. Risk models consider both inhalation and contact after ground impingement. To date over 400 samples have been collected and analysed for biologicals. We believe this to be a landmark study with respect to the evaluation of the potential for bioaerosols from land applied biosolids.

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SLUDGE QUALITY CRITERIA FOR AGRICULTURAL USE IN THE CONTEXT OF SOIL PROTECTION
by
Winfried E.H. Blum

Institute of Soil Research, University of Agricultural Sciences, Vienna, Austria

ABSTRACT
Soils have three important ecological functions:

- to produce biomass (e.g. food, fodder, renewable energy);

- to filter mechanically, buffer physico-chemically, and to transform (biologically/micro-biologically) substances between the atmosphere, the hydrosphere and the biosphere, thus protecting the food chain and the ground water (drinking water) against contamination, as well as soil biodiversity;

- Soil is the largest gene reserve existing on the globe.

Therefore, soil protection in the context of sludge application in agriculture, targets the maintenance of these three crucial functions for human societies and the environment.
Soil properties and processes differ widely (about 250 different soils in Europe alone), as well as the quality of sludges. Therefore, no general operational approach can be proposed for matching both substrates, soils, and sludges, but based on general assumptions, possibilities and constraints of sludge application can be assessed .
For agricultural use, some sludge contents, especially phosphorus, are increasingly important, due to the decrease of high quality P resources on a world-wide level. On the other side, sludges contain heavy metals and a broad range of organic compounds, including endogene disrupters, which have a considerable impact on the soil functions.
Therefore, different classes of sludge quality will be compared with medium and long-term reactions in soils, discussing conceptual approaches in future use of sludge in agriculture.

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Dentel